1. Field of the Invention
The present invention relates to a pneumatic tire improved in safety by keeping low rolling resistance and reducing static electricity generated during tire running.
2. Description of the Background Art
In recent years, various methods for using silica for a tread part, a breaker, a sidewall part, or the like of a tire have been proposed for the purpose of reduction in tire rolling resistance as well as of maintenance of wet grip performance. However, a problem of lack in safety is raised in the case where silica is contained in a large amount since electrical resistance of the tire is increased to generate spark due to static electricity, for example, during supply of fuel for a vehicle, so that the fuel catches fire. Therefore, there is a demand for a tire that realizes of a reduction in rolling resistance and maintenance of wet grip performance and is capable of preventing static electricity from being generated.
Japanese Patent Laying-Open No. 08-230407 discloses, as a pneumatic tire capable of improving electroconductivity and preventing discharge phenomenon caused by accumulation of static electricity in a vehicle body, a tire wherein: a rubber composition forming a tread part contains carbon black in a blending amount of 50 parts by weight or less with respect to 100 parts by weight of a rubber component and a non-carbon black reinforcing agent; a rubber component forming a sidewall part contains carbon black in a blending amount of 40 parts by weight or less with respect to 100 parts by weight of a rubber component; and an electroconductive thin film is disposed on the tread part and the sidewall part. It is disclosed in the publication that a rubber component forming the electroconductive thin film contains carbon black in a blending amount of 60 parts by weight or more with respect to 100 parts by weight of a rubber component and in a ratio of 35 wt % of the whole rubber composition.
Japanese Patent Laying-Open No. 2000-190709 proposes a pneumatic tire capable of maintaining excellent wet grip performance and effectively reducing tire electrical resistance as well as of stably exhibiting such characteristics from an initial use to a wear limit of the tire. The publication proposes a pneumatic tire, wherein a tread rubber includes a main tread rubber part that is made from an insulating rubber material having a volume specific resistivity of 1×108 Ω·cm or more and an outer electroconductive part that is made from a shoulder part electroconductive rubber material having a volume specific resistivity of less than 1×108 Ω·cm, forms a contact area together with a main tread part, and ends with a gap of 3% to 35% of a contact area margin in a tire axially inner direction from an edge of the contact area, the outer electroconductive part is in the form of a sheet having a thickness of 0.01 to 1.0 mm, exposed to a treat outer surface including a groove wall and a groove bottom of a lateral groove to be continuous in a tire circumferential direction; a wing rubber, a sidewall rubber, and a clinch rubber are formed of the shoulder part electroconductive rubber material; and the outer electroconductive part is continued to the wing rubber.
Japanese Patent Laying-Open No. 10-036559 proposes, as a tire sidewall rubber composition capable of rendering a tire having small rolling resistance, wear resistance, excellent wet performance, and small electrical resistance, a tire sidewall rubber composition obtainable by mixing and kneading 100 parts by weight of a specific diene-based rubber, 5 to 50 parts by weight of carbon black having a DBP oil absorption amount of 120 ml/100 g or less and a CTAB surface area of 130 μm2/g or less, 10 to 60 parts by weight of precipitated silica having a DBP oil absorption amount of 200 ml/100 g or more and a BET nitrogen adsorption specific surface area of 180 m2/g or less, and a silane coupling agent in an amount capable of controlling a reactive factor within a specific range.
Japanese Patent Laying-Open No. 08-034204 proposes a tire tread including a strip that is made from a tire tread rubber composition having a high resistivity by using silica as a reinforcing agent and has a predetermined side width while extending in a length direction and an electroconductive strip that spreads in the length direction in the side width and made from a tire rubber composition having a volume resistivity of 108 Ω·cm or less and a low resistivity.
However, in view of the methods in Japanese Patent Laying-Open Nos. 08-230407, 2000-190709, 10-036559, and 08-034204, there is a demand for improvement in satisfactory and excellent valance between low rolling resistance and high safety.